The present invention relates to a method for the production of patterned nonwoven fabric by sheet formation under hydraulic pressure treatment with high velocity water streams serving to cause fiber entanglement, and more particularly to such method for production of patterned nonwoven fabric comprising the steps of subjecting fibrous web to the hydraulic pressure treatment with high velocity fine water streams on water-impermeable supports to cause sufficient fiber entanglement in said fibrous web to form a sheet and then of subjecting this sheet to the similar treatment with high velocity fine water streams without deterioration of a strength of said sheet so that the entangled fibers may be reoriented by this last treatment to give the sheet a desired pattern.
It is well known to produce nonwoven fabrics by high energy treatment with water streams at unusually high pressure for fiber entanglement into a fibrous web. However, a mass production on a industrial scale has been difficult with this well known method, because only nonwoven fabric of unsatisfactory properties has been obtained with poor productivity and at a relatively high cost. In view of this situation, the inventors of the present invention have previously developed the effective method to improve the above-mentioned well known method and disclosed it in Japanese Patent Application No. 55-114151, U.S. patent application Ser. No. 293512 (now abandoned), GB Patent Application No. 8125263, West Germany Patent Application No. P31 32 792.3 and French Patent Application No. 81.16036. The invention thus disclosed in the applications in various countries was based on conditions that the supports for fibrous web should have a water-impermeability and a surface hardness of 50.degree. or higher as defined by JIS (the Japanese Industrial Standards)-K 6301 Hs; that each of the orifices adapted to jet the water streams at high pressure should have a vertical section comprising a diameter downwardly tapered portion and a linear small diameter portion, L/D, a ratio of the length L and the diameter of the former portion, being less than 4/1; that each of the water streams should be supplied transversely with respect to each of said supports at a flow rate of 40 cc/sec.cm or lower; that the pressure at which the water streams are jetted through the associated orifices should be lower than 35 kg/cm.sup.2 ; and that a basic weight of the fibrous web to be treated should be between 15 and 100 g/cm.sup.2.
It is also well known to produce patterned nonwoven fabric by a similar high energy treatment with water streams at high pressure. Such method also has drawbacks similar to those encountered by the above mentioned method.
In view of this situation, the inventors have developed an improved and novel method for production of patterned nonwoven fabric comprising continuous steps of the sheet formation by the fiber entangling treatment according to the previous invention of the inventors and of patterning. More specifically, the present invention is characterized by that, in the previously proposed method in accordance with said previous invention, there is provided as the fibrous web support of the final stage a support provided on its surface with a relief pattern so that the nonwoven fabric may be thereby correspondingly patterned.
The method according to the present invention thus enables patterned nonwoven fabrics of excellent properties to be produced at higher productivity and lower cost compared to the method of the prior art. The nonwoven fabrics obtained by the method of this invention have the bulkiness improved by the relief patterns and the surface gloss so matted that they look as if they are cotton fabrics. Thus, the cushiony, soft and warm touch of the product is remarkably improved. The relief pattern presents high density areas and low density areas so that the spot absorption capacity for liquid is also improved. The patterned nonwoven fabrics according to the present invention will find advantageous applications in a series of goods which are used in direct contact with the skin of the human body, for example, the surface material of a sanitary napkin or a disposable diaper.